This invention relates to a method of, and apparatus for, monitoring the radioactivity of a plurality of discrete areas of radioactive material on a surface region of a support layer.
Many experiments involve the study of the incorporation of radioactive chemicals into acid-precipitable material, for example the incorporation of radioactive thymidine into the DNA of lymphocytes. Some experiments involve the analysis of several hundred different test combinations, each performed in quadruplicate. Because of the length of time required to precipitate each of the cell cultures separately after incubation and the variability introduced by performing multiple manipulations of each culture, it is advantageous to utilize an apparatus which allows simultaneous precipitation of many samples with a minimum of sample handling. An example of such an apparatus is a cell harvester known under the Trade Mark "Titertek". This harvester is designed to harvest 12 microcultures at a time by means of 12 pairs of small tubes spaced to line up with a row of 12 wells in a 96-well microtitration plate. The microcultures are automatically precipitated on a glassfibre filter mat in the form of a regular 8 by 12 matrix configuration of small, regularly shaped areas of precipitate approximately 1 cm in diameter when all 96 microcultures have been harvested. If the microcultures are labelled with beta-emitting isotopes, the labelled cells are thus separated from the unincorporated isotope. The areas of precipitate typically occupy an area of 25 cm.times.8 cm.
It is known to monitor the radioactivity of the separate areas of precipitate as follows. Each of the 96 areas of precipitate are first separated, for example by punching out areas of the filter mat, and each portion of filter mat containing a respective area of precipitate is placed in a separate vial together with scintillation fluid. A scintillation counter is then employed to assess the radioactivity of the area of precipitate in each vial. Such a process is of course extremely time consuming, expecially if a large number of samples are to be processed. Furthermore, it is of course important that it should be known from which position on the mat each area of precipitate in each vial has been taken. Failure to label the vials correctly can lead to muddling of the samples.